The oxidation of naphthalene can produce phthalic anhydride, naphthoquinone, CO.sub.2 and H.sub.2 O. The present process is directed to a more selective production of the naphthoquinone, while minimizing the other by-products, such as phthalic anhydride.
The oxidation of naphthalene to make naphthoquinone is well known in the art. U.S. Pat. No. 1,844,387 issued in 1932 teaches the use of "non-silicious base exchange bodies" as catalysts for the vapor phase oxidation of naphthalene. The compounds useful for the catalysts are formed by reacting alkali metallates and metal salts. Salts of various metals, including copper, silver, beryllium, zinc, tin, lead, chromium, vanadium, iron, cobalt, platinum, palladium and the like, can be reacted with the metallates of many of the same metals, e.g. zinc, vanadium, tin, platinum and titanium.
U.S. Pat. No. 2,698,306 employs a catalyst for this oxidation process which consists of vanadium, tin and aluminum oxides with zirconium and titanium, optionally being employed in place of the tin. Tin oxide comprises from 50% up to 97% of the total weight of the catalyst. Other references employing vanadium oxides include U.S. Pat. Nos. 3,095,430; 3,402,187; 4,035,399 and 4,111,967. All of these also teach employing K.sub.2 SO.sub.4 ; some employ carriers such as silica, pumice, corundum, and silicon carbide. The '430 patent and also the '387 and '306 patents teach tin as a component of such catalysts. The '430 patent also teaches the use of porosity controlling agents such as graphite and urea and the '187 patent adds naphthalene or oxalic acid for the same purpose.